This invention relates generally to firearms and more particularly to the stock tube/spring/buffer combination used in automatic and semi-automatic rifles and carbines and the M16/AR15.
The M16/AR15 series of rifles was originally designed to use a twenty inch barrel; with the gas port located approximately thirteen inches from the breach. The original design also used an operating spring and buffer system designed specifically for the fixed stock.
As the battlefield changed, so too did the methods and tactics used by our military forces. These changes demanded that the individual weapon become shorter, more compact and easier to handle in confined spaces. This was ultimately accomplished by shortening the weapon's barrel and developing a telescoping stock system, which allowed the user to select varying degrees of “length of pull”. This telescoping stock system also used a new shorter action spring and was/is unable to use the existing action spring from the rifle version.
The new, shorter weapon is called a “carbine”. One of the shortcomings of the carbine is that when the barrel is shortened, the location of the gas port was also moved closer to the breach. The high pressure gases that are bled off at this port are what provide the energy for the weapon to operate; however, the gas pressures of the new shorter carbine system are nearly double what the original system was designed to do. This causes significantly higher operating pressures and forces the weapon to operate at much higher cyclic rates and with a noticeably increased bolt velocity.
To counter this, the carbine action spring is stiffer than the rifle action spring, and the functional length of the carbine spring is much shorter than the rifle spring. Attempts to run the longer rifle length barrel on a weapon with the shorter carbine length recoil system (collapsible stock tube, spring, and buffer) have proven to be an unreliable design.
This means that the two weapons, the rifle and carbine, require different combinations of stock tube, spring, and buffer in order to operate properly; otherwise, the weapons are not reliable; thereby forcing an expanded inventory of replacement and manufacturing parts.
It is clear there is a need for an improved stock tube/buffer/spring assembly to improve reliability and also decrease the complexity of the firearm systems.